DULUTH — Asian lady beetles congregate en masse in our homes each autumn. Emerald ash borers are eating their way across neighborhoods and forests. Gypsy moths are munching across the state from east to west on their way across North America.

But beware, Minnesota, you haven’t smelled anything yet.

Roll out the welcome mat for the next alien invader from afar, another unwelcome guest that arrived from Asia in packaging, probably in about 1996 near Allentown, Penn., and has been expanding across the continent ever since.

Meet the brown marmorated stink bug, a creature so foul that it will eat its way across fields of farm crops, orchards, gardens and vineyards and then congregate by the hundreds in your home to spend the winter.

And then when you try to kill it, the stink bug lives up to its name, emitting a smell that’s been compared to stale cilantro, rotten eggs, a teenager’s gym socks, paper mills, decaying flesh and even death.

The only good news is they can’t bite.

The Minnesota Department of Agriculture confirmed recently that the first brown marmorated stink bug in Duluth was reported in 2017 at the Apple Tree Circle Community Garden near the Duluth Zoo. It’s likely many more reports will come. After a lag period of several years since they were first found in Minnesota, bug experts say the state is on the cusp of a major stink bug outbreak.

“We’ve had them in Minnesota since 2010 around the Twin Cities. But it was just the last couple of years when we started getting reports of nymphs and adults. So they are established, they’re reproducing here,” said Angie Ambourn, entomologist and invasive species expert for the Minnesota Department of Agriculture.

Ambourn said it takes up to 10 years for the bugs to become established in new areas, depending on climate. Then their numbers explode. That’s what’s happened in Pennsylvania, Maryland, Virginia, West Virginia and other eastern states where they have caused millions of dollars in crop damages and disgusted untold homeowners.

In 2015 and 2016, Minnesota bug experts noted a major increase in the distribution and number of stink bugs in more counties and confirmed them on apples and soybeans. A computer map of their expansion across Minnesota tracks along major highways, including Interstate 35, with the invaders reported in orchards in Pine and Carlton counties in recent years.

Brown marmorated stink bugs from Asia are wreaking havoc on fruits and other crops across parts of the U.S., including apples and vegetables. (U.S. Department of Agriculture photo)

“They are notorious hitchhikers. They can ride on just about any vehicle — cars, trucks, RVs, delivery vans. They get into places where you can’t see them,” Ambourn noted. “They can cause some real damage to fruits and crops. … It’s not something we’re looking forward to in the coming years.”

Perhaps the most noticeable impact of brown marmorated stink bugs is their tendency to congregate in homes by the hundreds. When a few get in, they emit a pheromone that attracts even more, and they tend to congregate in giant clusters. This indoor flocking starts in autumn, and then the bugs go into a sort of insect hibernation or stupor.

As winter turns to spring, the bugs begin to wake up.

“We’re starting to get calls now from people who are seeing them moving inside their homes. As the sun starts to hit houses a little more now, they are waking up,” Ambourn said last week.

The bugs have a reputation for entering any tiny nook or cranny to get into a home or building (outlets, light fixtures, under vinyl and even wood siding) where they hide behind drapes and curtains, in attics, even in closets and drawers. They tend to avoid basements and go to the highest part of the building. (Rutgers University in New Jersey found stink bugs in about 10 percent of dorm rooms on ground floors but nearly 70 percent on upper-floor rooms.)

In eastern states, so far, it appears the bugs have cycles, where their population moves up and down over years. As of yet, however, nothing has eliminated the bug from any area they have infested. Pesticides, even in extremely high doses, have proven only partially effective. There was speculation that the insect couldn’t survive cold winters. But it’s now established in Minnesota and it’s been found in Ontario, Quebec and British Columbia.

A tsunami of stink

Brown marmorated stink bugs “are like a lot of invasive species in that they get here, it takes a while to build up, and then there’s this tsunami that’s been rolling across the country, and it’s about to roll over you in Minnesota,” Mike Raupp, University of Maryland Extension entomologist, told Forum News Service.

Entomologists from the Minnesota Department of Agriculture and University of Minnesota are seeking funding from the Minnesota Environment and Natural Resources Trust Fund to test whether Asian stingless wasps (called the samurai wasp) that focus on brown stink bugs can be used here to keep stink bug numbers in check. Similar stingless wasps are being used in an effort to control emerald ash borers, also imports from Asia.

The samurai wasp was already showing up in the U.S. before scientists started looking at introducing more. They lay eggs in stink bug eggs and eventually reduce stink bug numbers enough to curb the population.

With many invasive species, after their numbers explode, they crash. That’s happened in several eastern states where stink bugs haven’t been a major plague for several years. No one is quite sure what spurs their population cycles.

“It’s a little bit like ‘Goldilocks and the Three Bears.’ If it gets too cold, or too hot, that knocks them back. They need (temperatures) to be just right,” Raupp said, noting the rapid onset of the Polar Vortex winter of 2013-14 seemed to markedly reduce, but not eliminate, stink bug numbers in eastern states.

With temperatures over 90 degrees, Raupp said, a bacteria that protects the young stink bug’s gutt is damaged and the bugs die.

“You probably aren’t going to get to 90 degrees in May or June, so I think your best bet up there is when you get those rapid cold snaps, down into the teens, before the bugs can get into their dead trees or cliff sides or into your houses. If the deep cold comes before they’re ready for winter, that can really put a beatdown on them,” Raupp said. “But if you have a gradual winter onset, they can survive just fine.”

The good news in eastern states, Raupp noted, is that several native predators have started to prey on stink bugs, including spiders, native parasitic wasps, a creature called the wheel bug and Chinese praying mantis (an invasive from Asia that came here a century before stink bugs). But that may not help in Minnesota quite yet. It often takes native predators several years to start keying on invasives, he noted.

“You’re going to get brown marmorated stink bugs,” Raupp said. “It’s just a matter of how bad and how long until a predator or the weather catches up to them and they drop to a tolerable level.”

What’s all the stink about?

Brown marmorated stink bugs come from Asia, including China, Korea and Japan. They are one of 4,700 species of stink bugs in the world, including 250 in North America that are generally kept in check by natural predators and which don’t become major problems.

The Asian imports are known to feed on over 300 different species of plants, including many fruits, vegetables and crops. The damage from their piercing-sucking mouthparts can lead to significant crop loss. Threatened crops in Minnesota include apples, grapes, corn, soybeans and garden vegetables like tomatoes, peppers and peas.

To survive the winter they take cover in trees and, where available, in houses, garages or barns. They can become a nuisance in fall when many bugs can invade a home, and in spring when they wake up from a winter’s nap.

Stink bugs smell bad. The smell is often described as earthy, some say it resembles a very strong cilantro odor, others have compared it to rotting flesh. This defensive liquid is secreted from the underside of their thorax when the stink bugs feel threatened, or when they are squished.

The stink bugs’ range keeps expanding as they hitchhike on cars, trucks, campers, in suitcases and even in mailed packages. In Minnesota their expansion has followed major highways.

Experts say to seal all potential entryways into your home with caulk or other material. To remove the bugs, use a vacuum. But be warned that the vacuum could start to smell as bad as the bugs.

Adults are about the size of a dime, brown with mottled or marbled patches on them. Nymphs (young) are more colorful, with red and orange markings. Other key features are the rounded shoulders, the alternating dark-and-light pattern along the edges of the abdomen, the dark-colored antennae with light-colored bands.

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